The present invention relates to an olefin thermoplastic elastomer, a process for producing the olefin thermoplastic elastomer and use of the olefin thermoplastic elastomer. More particularly, it relates to an olefin thermoplastic elastomer suitable for melt molding of irregular shaped corner connections or irregular shaped end parts such as a weather strip, door trim and the like for automobiles, a process for producing the same and use thereof.
Conventional production of weather strips having a connection is generally carried out by cutting extrusion vulcanized molded articles of a rubber compound of an ethylene/propylene/non-conjugate diene terpolymer (EPDM), setting them in a mold from one side or both sides to form a cavity, injecting the same kind of a rubber molding material as this EPDM rubber compound into the cavity and performing vulcanizing molding.
Further, from the viewpoint of productivity, environmental adaptability and weight saving, a thermoplastic elastomer (composition) for which a vulcanization step is unnecessary has been used as materials of the molding in place of the vulcanized rubber prepared by using an ethylene/propylene/non-conjugate diene terpolymer (EPDM).
In general, vulcanization bonding or the like between a vulcanized rubber and a thermoplastic elastomer can be not conducted so that integration thereof has been conducted by means of an adhesive. However, it is not said that the integration with an adhesive is sufficient in view of productivity and environmental adaptability.
As the technique of a thermoplastic elastomer composition, addition of a polar group-containing resin can be described in JP-A-2(1990)-115249, JP-A-8(1996)-244068 and JP-A-10(1998)-324200. In the case of the addition of the polar group-containing resin, releasability of a molded article from a mold is lowered and thereby a molding cycle is prolonged.
As another technique, a technique that a specific ethylene/1-octene copolymer is added before molding a thermoplastic elastomer is disclosed in JP-A-9(1997)-40814. Although the present inventors confirmed that this technique is very effective against base material breaking, the rubber elasticity of molded articles is missing due to addition of a non-cross-linked ethylene polymer (ethylene/1-octene copolymer).
As a further technique of the vulcanized rubber, a technique of adding finely crystalline polyprolylene in addition to the conventional vulcanized rubber composition is disclosed in JP-A-10(1998)-7849. However, when finely crystalline polypropylene such as atactic polypropylene is added, not only rubber elasticity which the conventional vulcanized rubbers have is lowered but also tackiness of molded articles is induced occasionally with the elapse of time.
In addition to the techniques regarding the thermoplastic elastomers and the composition of vulcanized rubbers, there are a technique of obtaining anchoring effect by making a cut surface rough after cutting a vulcanized rubber (JP-A-9(1997)-118133) and a technique of applying a powdery polyolefin resin on the cut surface of a vulcanized rubber (JP-A-6(1994)-47816). Any of the above techniques, however, have a defect such that the adhesion is not improved for lowering in productivity.
Accordingly, it has been desired that an olefin thermoplastic elastomer having sufficient bonding strength to vulcanized rubbers without through an adhesive layer and capable of forming molded articles having such a characteristic that at peeling a base material is broken, that is, any of molded articles are broken but the molded articles are not broken at the interface thereof, and molded articles obtainable by melt bonding the elastomer with a vulcanized rubber be realized. Additionally, it has been desired that an olefin thermoplastic elastomer having sufficient hardness as a thermoplastic elastomer and capable of forming light weight molded articles with rubber elasticity, and having excellent moldability and economic properties, and molded articles obtainable by melt bonding the elastomer with a vulcanized rubber be realized.
The present invention is intended to solve the problems associated with the prior art. It is an object of the invention to provide an olefin thermoplastic elastomer having sufficient bonding strength to vulcanized rubbers by no way of an adhesive layer and capable of forming molded articles having such a characteristic that at peeling a base material is broken, and to provide molded articles obtainable by melt bonding the elastomer with a vulcanized rubber. It is another object of the invention to provide an olefin thermoplastic elastomer having sufficient hardness as a thermoplastic elastomer and capable of forming light weight molded articles with rubber elasticity, and having excellent moldability and economic properties, and to provide molded articles obtainable by melt bonding the elastomer with a vulcanized rubber.
It is a further object of the invention to provide a process for preparing the above olefin thermoplastic elastomers.
The first olefin thermoplastic elastomer of the invention is an olefin thermoplastic elastomer, which forms an islands-sea structure, and has a particle phase having an average particle diameter of less than 2 xcexcm, a gel fraction of from 0.5 to 15% by weight and a quantity of heat of melt at a temperature of 125xc2x0 C. or below, as measured in a Differential scanning calorimeter (DSC), of 40% or more based on the total quantity of heat of melt.
The thermoplastic elastomer comprises an olefin resin and an olefin rubber and the olefin rubber is cross-linked.
The first olefin thermoplastic elastomer of the invention has a quantity of heat of melt, as measured in a differential scanning calorimeter (DSC), (which is the same as the above total quantity of heat of melt) of preferably 30 J/g or more.
With regard to the first olefin thermoplastic elastomer of the invention, the proportion of the islands phase having a ratio of major axis to minor axis of two or more is preferably not more than 3% based on the total of the islands phases, and the compression set (CS) at 70xc2x0 C. is preferably not more than 65%. This compression set at 70xc2x0 C. is an index of rubber elasticity.
The first olefin thermoplastic elastomer of the invention is obtainable by dynamically vulcanized an olefin resin and an olefin rubber in the presence of a cross-linking agent and preferably satisfies the following relation:
Axc3x97CS less than 5.0 
wherein A is an amount (part by weight) of a cross-linking agent for adding based on the total amount (100 parts by weight) of the olefin resin and olefin rubber, and CS (%) is a compression set at 70xc2x0 C., which is an index of rubber elasticity.
The second olefin thermoplastic elastomer of the invention is prepared from a blend comprising:
5 to 50 parts by weight of a high-density polyethylene (A1) having a density (ASTM D 1505) of 0.940 g/cm3 or more,
5 to 70 parts by weight of an ethylene/xcex1-olefin (/non-conjugated polyene) copolymer rubber (B) comprising ethylene, an xcex1-olefin of 3 to 20 carbon atoms and optionally a non-conjugated polyene, and
5 to 50 parts by weight of a polypropylene (C), provided that the total of the components (A), (B) and (C) is 100 parts by weight, and has a gel fraction of from 0.5 to 15% by weight.
With regard to the second olefin thermoplastic elastomer of the invention, the high-densitypolyethylene (A1) preferably has a melt flow rate at 190xc2x0 C. (MFR; ASTM D 1238 under a load of 2.16 Kg) of not more than 10 g/10 min.
The second olefin thermoplastic elastomer of the invention is an olefin thermoplastic elastomer having an islands-sea structure, and desirably has a particle phase having an average particle diameter of not more than 2 xcexcm, a gel fraction of from 0.5 to 15% by weight, and a quantity of heat of melt at a temperature of 125xc2x0 C. or below, as measured in a differential scanning calorimeter (DSC), of 40% or more based on the total quantity of heat of melt. The second olefin thermoplastic elastomer of the invention has a quantity of heat of melt, as measured in a differential scanning calorimeter (DSC) of preferably 30 J/g or more.
The process for producing the second olefin thermoplastic elastomer of the invention comprises melt blending, in the presence of a cross-linking agent (D), a blend comprising:
5 to 50 parts by weight of a high-density polyethylene (A1) having a density (ASTM D 1505) of 0.940 g/cm3 or more,
5 to 70 parts by weight of an ethylene/xcex1-olefin (/non-conjugated polyene) copolymer rubber (B) comprising ethylene, an xcex1-olefin of 3 to 20 carbon atoms and optionally a non-conjugated polyene, and
5 to 50 parts by weight of a polypropylene (C), and thereby a thermoplastic elastomer having a gel fraction of from 0.5 to 15% by weight is obtained.
The cross-linking agent (D) is preferably an organic peroxide.
The third olefin thermoplastic elastomer of the invention is prepared from a blend comprising:
5 to 40 parts by weight of a crystalline ethylene polymer (A2) having a crystallinity as measured in DSC method of not less than 10% and a density (ASTM D 1505) of less than 0.940 g/cm3,
5 to 70 parts by weight of an ethylene/xcex1-olefin (/non-conjugated polyene) copolymer rubber (B) comprising ethylene, an xcex1-olefin of 3 to 20 carbon atoms and optionally a non-conjugated polyene, and
5 to 40 parts by weight of a polypropylene (C), provided that the total of the components (A2), (B) and (C) is 100 parts by weight, and has a gel fraction of from 0.5 to 15% by weight.
The third olefin thermoplastic elastomer of the invention is an olefin thermoplastic elastomer having an islands-sea structure, and desirably has a particle phase having an average particle diameter of not more than 2 xcexcm, a gel fraction of from 0.5 to 15% by weight, and a quantity of heat of melt at a temperature of 125xc2x0 C. or below, as measured in a differential scanning calorimeter (DSC), of 40% or more based on the total quantity of heat of melt. The third olefin thermoplastic elastomer of the invention has a quantity of heat of melt, as measured in a differential scanning calorimeter (DSC) of preferably 30 J/g or more.
The process for producing the third olefin thermoplastic elastomer of the invention comprises melt blending, in the presence of a cross-linking agent (D), a blend comprising:
5 to 40 parts by weight of a crystalline ethylene polymer (A2) having a crystallinity as measured in DSC method, of not less than 10% and a density (ASTM D 1505) of less than 0.940 g/cm3,
5 to 70 parts by weight of an ethylene/xcex1-olefin (/non-conjugated polyene) copolymer rubber (B) comprising ethylene, an xcex1-olefin of 3 to 20 carbon atoms and optionally a non-conjugated polyene, and
5 to 40 parts by weight of a polypropylene (C), provided that the total amount of the components (A2), (B) and (C) is 100 parts by weight, and thereby a thermoplastic elastomer having a gel fraction of from 0.5 to 15% by weight is obtained.
The cross-linking agent (D) is preferably an organic peroxide.
The first, second and third olefin thermoplastic elastomers according to the present invention are suitable for use in melt bonding to a vulcanized rubber molded article.
The first, second and third olefin thermoplastic elastomers are preferably a thermoplastic elastomer which causes base material breakage at tensile peeling in a melt bonding test of a vulcanized rubber press molded article with any of the first, second and third olefin thermoplastic elastomers.
The molded articles of the invention are obtainable by joining (bonding) a vulcanized rubber molded article to a molded article of any one of the first, second and third olefin thermoplastic elastomers.
The molded articles of the invention are preferably obtainable by melt bonding the vulcanized rubber molded article to any one of the first, second and third olefin thermoplastic elastomers.
The vulcanized rubber is preferably an ethylene/xcex1-olefin/polyene copolymer rubber.
The molded articles of the present invention are suitably used for automobile interior and exterior materials. For example, they are suitably used for weather strip materials. Specifically, there is a molded article of a weather strip material prepared by joining (bonding) a linear part and a (joint) corner element (portion) wherein the linear part comprises the vulcanized rubber molded article and the corner element comprises any one of the first, second and third olefin thermoplastic elastomers.
The molded articles prepared by melt bonding the vulcanized rubber molded article with any one of the first, second and third olefin thermoplastic elastomers are obtainable by, for example, insert molding.
The molded articles of the invention are preferably molded articles, which result in base material breakage when the tensile peeling test on the joined parts of the molded articles is carried out.
Any one of the first, second and third olefin thermoplastic elastomers according to the invention has sufficient bonding strength to vulcanized rubbers by no way of an adhesive layer and can form molded articles which result in base material breakage at peeling and further, can form light weight molded articles having sufficient hardness and rubber elasticity as a thermoplastic elastomer.